Free piston gas generators



July 13, 1 M. BOUVIER ETAL 3,194,007

FREE PISTON GAS GENERATORS Filed July 7, 1964 5? I37 I 36 Z1 Z0 3 31 E926' ]9;O J6 J4 in; J3

I77 I II 11.,

INVENTOR United States Patent Office 3,1943%? Patented July 13, 19553,194,007 FREE PISTON GAS GENERATORS Maurice Bouvier, Villeurbanne, andAuguste Moiroux,

Lyons, France, assignors to Societe dEtudes et de Participations, Eau,Gaz, Eleetricite, Energize S.A., Geneva, Switzerland Filed July 7, 1964,Ser. No. 380,833 Claims priority, application France, July 25, 1%3,942,695 3 Claims. (Cl. 60-13) The present invention relates to freepiston gas generators, or auto-generators, comprising a stabilizerserving to adapt the mass of air present in the return energy pneumaticaccumulators (hereinafter called cushions) to the variations of the loadunder which the gas generator is working.

For this purpose, it is known to have the stabiliser controlled, on theone hand, by a factor depending upon the load of the gas generator, thisfactor generally being the pressure existing in the air reservoir, orcasing, disposed between the compressor unit of the gas generator andthe motor unit thereof, and, on the other hand, by a pressurecharacteristic of the cushion, or cushions, this characteristic pressurebeing for instance either the mean value of the instantaneous pressuresexisting in said cushion, or cushions, or a pressure collected from thecushion, or cushions, when the free piston, or pistons, is, or are, in apredetermined position with respect to the fixed unit of the gasgenerator.

It is also known to arrange the stabiliser in such manner, that, whenthe load of the gas generator increases, the mass of air in the cushion,or cushions increases so as to produce an increase of the finalcompression pres sure in the motor unit of the gas generator andinversely, which has for its effect to increase the number ofreciprocations per unit of time of the generator pistons when the loadof the generator increases and to reduce this number when this loaddecreases. Such a variation of the number of strokes of the pistons perunit of time permits of reducing the variations of length of saidstrokes which are necessary to take into account variations of the loadunder which the gas generator is working.

It is also known further to increase the variation of the finalcompression in the motor unit and, consequently, the variation of thenumber of strokes per unit of time, by connecting with that of thechambers of the stabiliser where the pressure is determined by thecharacteristic pressure of the cushion, or cushions, a leak theinfluence of which increases when the load of the gas generatorincreases and inversely. The object of this leak is to weaken theinfluence of the characteristic pressure of the cushion upon thestabiliser and to delay the resetting of said stabiliser into neutralposition, where it closes the cushion or cushions. Up to the presenttime, this leak was controlled in response to variations of the lengthof the strokes of the free piston or pistons, and this in such mannerthat the leak, between two consecutive strokes of said piston orpistons, remained open the longer as .the stroke was longer. Howeverthis manner of controlling the leak involved some drawbacks. First itrequired maintaining a relatively important difference between thelengths of the strokes of the free piston or pistons. Furthermore it didnot permit of compensating for the influence of some defects influidtightness capable 'of varying the control pressure acting in thestabiliser in response to variations of the characteristic pressure ofthe cushion.

The chief object of the present invention is to obviate this drawback.

The invention consists chiefly in having the diiference between, on theone hand, the characteristic pressure of the cushion, such as it existsin said cushion or just at the outlet thereof, and, on the other hand,the pressure depending upon this. characteristic pressure and actingupon the stabiliser, controlled by the member the position of whichdetermines the amount of fuel injected into the motor unit of the gasgenerator.

Preferably the chamber of the stabiliser subjected to the effect of thepressure varying as a function of the characteristic pressure of thecushion is provided with a leak opening adapted to be opened or closedby an element moving together with the fuel regulating member, thisopening being provided on a movable support which is subjected, on theone hand, to the characteristic pressure of the cushion at the outletthereof, that is to say when it is not yet reduced by a disengagement ofsaid leak opening and on the other hand to the pressure reduced by saiddisengagement or of the leak opening, a spring being further provided toadd its action to that of said reduced pressure.

A preferred embodiment of the present invention will be hereinafterdescribed with reference to the appended drawing, given merely by way ofexample, and which diagrammatically shows, in longitudinal section, agas generator according to the invention.

Thus, the gas-generator illustrated in the drawing comprises at leastone compressor cylinder 1 and one motor cylinder 2, and a pistonassembly formed by a compressor piston 3 and a motor piston 4, whichpistons operate in cylinders 1 and 2, respectively.

The part of cylinder 1 adjoining motor cylinder 2 is provided with inletvalves 5 and delivery valves 6, the latter being fitted in a partition 7which forms the internal head plate of compressor cylinder 1 and whichseparates the same from a scavenge air reservoir 8 forming a casingsurrounding motor cylinder 2. The compressor cylinder proper is formedby a chamber or located between piston 3 and partition 7. On the otherhand, the pneumatic return energy accumulator or cushion is formed by achamber b located between the head 9 of compressor cylinder 1 andcompressor piston 3.

Intake ports 10 and exhaust ports 11, controlled by motor piston 4, areprovided in the wall of motor cylinder 2. Connected to the exhaust ports11 is an exhaust pipe 12 through which the power gas constituted by theexcess of scavenging air and the combustion gas of the motor cylinder isconveyed to a receiving machine such as a turbine (not shown).

Motor cylinder 2 is fitted with a fuel injector 13 supplied from aninjection pump 14 through a pipe 15. The compression which is producedin motor cylinder 2 when the piston assembly 3, 4 has terminated itsinward stroke (to the right in the drawing) is high enough for the fuelinjected by injector 13 to be ignited by the heat of compression alonewithout the use of any special ignition device. The motor unit is atwo-stroke engine operating on the diesel principle.

In the gas-generator illustrated in the drawing, injection pump 14 isdriven by means of a rocking lever 16 oscillating about an axis 17 andwhich is driven by the piston assembly 3, 4 through the agency of rod 18and link 19.

For the sake of simplicity in the description and drawing, agas-generator having only one piston assembly 3,

4 has been described and illustrated but, as is usual .in

practice, the gas-generator will generally comprise two such assemblieswhich move in opposed directions in a single motor cylinder, thecompressor pistons operating in compressor cylinders disposed on eitherside of the motor cylinder. Of course, the invention is applicable tothe latter kind of gas-generator.

The means for controlling the quantity of fuel injected into motorcylinder 2 comprise a regulating member 20 which determines the quantityof fuel delivered per cycle by pump 14 and injected through injector13'. In known 'manner, said member 20 consists of a toothed rack whichoperates the piston (not shown) of the piston pump. Rack 20is'controlled, in known manner, to increase or decrease'the fuel deliveryby means, of a regulator (not shown) driven by the receiving machine(turbine) and acting on ,said rack 20 through a linkage, or, throughhydraulic, electrical, or other means, in dependence upon the speed ofthe' receiving rtnach'ine. However, this control in dependence upon thespeed of the receiving machine must remain within limits whose values.are dependent upon the, operating pressure, or a similar operatingfactor, of the gas-generator, such limits being defined by a lever 21adapted to rotate around a spindle 22 and having one of its endsarticulated to the control linkage of member I .20, the other end of thelever 21. comprising two cam surfaces 23, 24 and a stop 25 beingprovided between said cam surfaces 23and 24, the position of thestop 25beingcontrolled by means tobe described hereinafter. The amount of airin cushion b is controlled by a device, known as a stabiliser andcomprising a hollow slide valve 26 adapted to move in.a cylinder 27disposed inside casing 8., Slide valve 26 is divided by a partition intotwo chambers, one of which is provided with check valves 28 which onlyopen in such a Way as to allow the passage of air from the casing 8'into slide valve 26 while the check valves '29; of the other chamberopen only in the opposeddirection so that air can flow out of slidevalve 26 into the casing 8. The lateral wall of each of the two chambersis formed with an aperture 30, 31, these apertures serving, according tothe axial position of slide valve 26, to connect one or the other of thelast mentioned chambers to a pipe 32 connecting cylinder 27 with acushion b. Slide valve 26, inits central position (that shown in thefigure), cuts off its two chambers completely from pipe 32. Thus,according to its axial position, slide valve 26 either allows air toescape from cushion b into casing "8 through check valves 29 orpermits-air to I return from casing 8 into cushion b through checkvalves 28 or it causes the quantity of air in accumulator b to bemaintained constant. 7 V s The stabiliser just described is controlledonthe one hand by. the action of the pressure existingin casing and on theother-hand by'the action of a pressure depending upon a characteristicpressure of cushion b and lower than it. The above mentionedcharacteristic pressure may be for instance either the mean pressure ofthe cushion or the pressure existing therein when piston occupies agiven position. These pressures act upon ,a stepped differentialpiston-33 rigidly secured to slide valve 25 and one '5 of the surfaces.9; of which is subjected to the pressure depending upon thecharacteristic pressure of cushion b whereas its other surface sissubjected to the pressure existing in casing 8. Piston 33 is disposedin a cylinder 34 to which are connected, on the'one hand, a pipe 35 forplacing the top of cylinder 34 in communication with casing 8 and, onthe other hand a pipe 36 through which the pressure existing in casing8, increases, and vice .versa,

In order further to increase this eifect, the area a, of

piston'33 is subjected, not directly, to said characteristic pressure ofthe cushion but. to apressure depending upon said characteristicpressure and lower thancit, the difference between the characteristicpressure and the pressure deduced therefrom increasing when the load ofthe pressure generator increases and decreasing in the reversecase.--'-'- In the embodiment illustrated by the drawing, thecharacteristic pressure of cushion bis equal to the meanvalue passage33. through conduit 36 to the surface s pf piston 33 to a of theinstantaneous pressures existing in said cushion. For this purpose,there, is connected with cushion b a conduit 37 communicating withconduit -36 through a throttled In order to reduce the pressuretransmitted value below the mean pressure in cushion b, a shunt conduit39 is connected to conduit 36'downstream of throttled passage38. Thisshunt conduit 39 leads to a leak opening 40 itself controlled by asleeve 41 operatively cono nected with therack 20 serving to control theamount of fuel injected into the power, cylinder 2 of thepressuregenerator. The'means forcontrolling leak orifice 40 are arrangedin suchmanner as to produce between, on the one, hand, the pressure acting uponthe surface s of piston '33 and, on the other hand,'the mean value ofthe. in-

stantaneous pressures of cushion b a difference which is the moreimportant as the position of rack corresponds to a more important amountof fuel injected into motor cylinder 2 at the end of every inward strokeof 20 pistons 3- 4.

v For this purpose, leak orifice 401is provided at the end of aconduit142 formed 'in'a rod 43 and the end 1 of which opposed to leakorifice 40 opens into a chamber A 45 which is connected, through conduit39, with conduit 36. Rod 43 is controlled bya piston46 movable in acylinder 47 the lower portions of whichforms said chamber '45. Piston46' has one ofits sides subjected to the action of the pressure existingin chamber 45 and its other side subjected to the action of thecharacteristic pressure of cushion b. In the embodiment illustrated bythe drawing, this characteristic pressure is transmitted to space 48,disposed inside cylinder 47 above piston 46, through a'conduit 49 branching ofi' from conduit 37 at a point up- 'stream of throttled passage38 so that the pressure in space 48 is substantially equal to the meanpressure of cushion b. V

Rod 43 is further subjected to the action of a spring 51. One. of theends of this spring 51, bears against the under face of the head 52 ofrod 43, whereas the other end of spring 51 bears against the fixedbottom 53 of cylinder 47. This spring 51, by keeping the head 52 of rod43 constantly applied against piston 46, acts on the latter in the samedirection as the pressure existing in chamber 45. a a

As already stated, the amplitude of the movements of ,rack 20v islimited by abutment 25 whichfis located between cam surfaces 23 and 24.However, this limitation 'must vary with the pressure existing in casing8. For this. purpose 'abutment'25is supportedby one end of O a rod 54,the other end of which is secured to a piston 56 movable in acylinder57'. This cylinder isconnected through a conduitl58; to conduit 35, sothat the pressure in casing 8 acts on one of the sides of piston 56 theother side of which is subjected to the action of a r eturn spring 59.

' The operation of said means for controlling the leak is asfollows: v I

When, due to an increase of the load of the plant to which the pressuregenerator belongs, rack 26 is moved,

, 6 for instance, by the. regulating device of the turbine to which thegases from the generator are fed, in the direction of the arrow thisdisplacement produces, on the one hand, an increase of the'amount offuel injected into the power cylinder and, on the other hand, adisplacement of sleeve 41 so. that the free section of leak opening v40is increased. a r

' This increase of the amountof fuel that is injected produces anincrease of the pressure in the casing, whereby the stabilizer isdisplaced in a direction which permits compressed air to flow throughconduit 32 into cushion b.

w On-the other hand the increase of the cross section of leak orifice 40causes the pressure to drop in chamber 45, so that piston 46,under'theeffect of'the characteristic'pressure in cushion b which has notdecreased, transmitted to space'48, moves in the downward directiontogether with rod 43, thus compressing spring 51. This displacementagain reduces the cross section of leak 40. Of course the inflow of airinto cushion b increases the characteristic pressure therein (in thiscase the mean pressure therein), which causes a rise of the pressureboth in chamber 45 and in space 48. However the difference between therespective pressures in said chamber and said space increases more andmore as rack 20 is moved in direction in view of the fact that when anew state of equilibrium is reached the compression of spring 51 hasincreased. This results from the fact that in order to have piston 46once more in the balanced state it is necessary to have P being thepressure force exerted by the characteristic pressure of cushion b inspace 48 upon piston 46, P being the pressure force exerted in chamber45 upon said piston 46 by the pressure therein, which is reduced by theexistence of the leak orifice 40 and R being the force exerted by thespring upon orifice 40 and R being the force exerted by the spring uponpiston 46. Consequently the greater the value of R the higher thedifference between P and P In view of the fact that P (pressure derivedfrom the mean pressure) is at the same time the pressure acting upon thesurface s of piston 33 it follows that this pressure P is the smallerwith respect to the mean pressure of the cushion as rack 20 has beenmoved to a greater distance in the direction corresponding to anincrease of the amount of fuel that is injected.

It should be reminded here that, in the case of an increase of the massof air into cushion b, the increase of the pressure derived from thecharacteristic pressure in said cushion b and acting upon the surface .9of piston 33 is intended to bring the movable element 26 of thestabiliser into the neutral position, where it closes conduit 32 after agiven mass of air has flown into cushion b. Owing to the presentinvention, this closing is delayed and the mass of air that is admittedinto cushion b is increased with respect to what would take place if thecharacteristic pressure acted directly upon the surface s of piston 33instead of making use of the pressure reduced by leak orifice 40. Thisincrease of the mass of air is the more important as the displacement ofrack 2% in direction is greater.

In case of a decrease of the load of the pressure generator, the resultis reversed. This means that the difference between the characteristicpressure of the cushion and the pressure derived from saidcharacteristic pressure decreases when the load decreases.

The invention has many advantages.

First it permits of reducing the variations of length of stroke of thefree pistons as much as it may be desired. Furthermore, there isobtained an automatic compensation of the uncontrollable leaks whichmight have an influence upon the pressure acting upon the surface s ofpiston 33. These leaks may take place for instance between the twochambers limited in cylinder 34 by surfaces s and s either at the placewhere the rod that connects piston 33 with sliding member 26 passesthrough the end wall of cylinder 34, or at the place where rod 43extends through the end wall 53 of chamber 45', or again between spaces45 and 48 which are separated from each other by piston 46 in cylinder47.

In view of the fact that, in the balanced state of the system, leakorifice 40 is always slightly open, the existence of uncontrollableleaks merely has for its effect slightlyto reduce the free cross sectionof opening 40, this reduction being the more important as thenoncontrollable leaks are also important.

Finally, another advantage consists in the fact that the mass of air ofthe cushion cannot undergo too quick variations since the amplitude ofthe movement of sleeve 41 which controls leak orifice 4G is limited inthe same manner as the amplitude of the movements of rock 20 6 itself bythe cooperation of abutment 25 with cam surfaces 23-24.

According to a modification, the part which controls the free section ofleak orifice 40 is actuated through the means, generally consisting of avariable pressure liquid for transmitting the control pulses of theregulating device of the turbine fed by the pressure generator to thepart (generally rack 20) which determines, by its position, the amountof fuel injected to the motor unit of the gas generator.

In a general manner, While the above description discloses what isdeemed to be a practical and eflicient embodiment of the presentinvention, said invention is not limited thereto as there might bechanges made in the arrangement, disposition and form of the partswithout departing from the principle of the invention as comprehendedwithin the scope of the appended claims.

What we claim is:

1. A free piston auto-generator which comprises, in combination, a motorunit and a compressor unit, said motor unit including two motorelements, a motor piston and a motor cylinder, one movable in the otherto form between them a variable volume fuel combustion chamber, fuelfeed means opening into said fuel combustion chamber, means forcontrolling said fuel feed means, said compressor unit including twocompressor elements, a compressor piston and a compressor cylinder, onemovable in the other, each of said compressor elements being fixed withrespect to one of said motor elements, respectively, a casing fixed withrespect to said motor cylinder, for feeding compressed air thereto, saidcompressor elements forming between them an air compression chamber,check valve means for admitting air from the atmosphere into said aircompression chamber on every increase of volume of said air compressionchamber, check valve means for delivering compressed air from said aircompression chamber to said casing on every reduction of volume of saidair compression chamber, said compressor elements forming between theman air cushion chamber the volume of which is reduced on every increaseof volume of said fuel combustion chamber, whereby expansion of said aircushion produces every return stroke of said motor piston, a conduithaving one end thereof in communication with said air cushion chamber, astabiliser valve mounted to control the communication between the otherend of said conduit and said casing, said stabiliser valve including acylindrical housing, a hollow slide valve slidable in said casing andhaving a neutral position therein and check valve means carried by saidslide valve arranged to open a unidirectional communication from saidcasing to said conduit when said slide valve is moved in one directionfrom said neutral position thereof and a undirectional communicationfrom sad conduit to said casing when said slide valve is moved in theother direction from said neutral position thereof, means operative by apressure at least substantially proportional to the pressure in saidcasing for urging said slide valve in said first mentioned direction,means forming a space containing air under pressure supplied from saidair cushion chamber, means operative by the pressure in said space forurging said slide valve in said second mentioned direction, variable airleak means in communication with said space and means for controllingsaid air leak means operative by said means for controlling said fuelfeed means, said means for controlling said air leak means beingarranged to tend to increase the free cross section of said air leakmeans when said means for controlling said fuel means is caused toincrease the feed of fuel and to tend to reduce said free cross sectionwhen the feed of fuel is decreased.

2. A free piston auto-generator which comprises, in combination, a motorunit and a compressor unit, said motor unit including two motorelements, a motor piston and a motor cylinder, one movable in the otherto form between them a variable volume fuel combustion chamber, fuelfeed means opening into said fuel combustion chamume of said aircompression chamber, check valve means for'delivering compressed airfrom said air compression chamber to said casing on every reduction ofvolume of said air compression chamber, said compressor elements formingbetween them an air cushion chamber the volume of which is reduced onevery increase of volume of said fuel combustion chamber, wherebyexpansion of said air cushion produces every return stroke of said motorpiston, a conduit having one end thereof in communication with said aircushion chamber, a stabiliser, valve mounted to control thecommunication between'the other end of said conduit and said casing,said'stabiliser'valve including a cylindrical housing, a hollow slidevalve slid.-

able in said casing and having a neutral position therein and checkvalve means carried by said slide valve arranged to open a unidirectionlcommunication from said casing to said conduit when said slide valve ismoved in one direction from said neutral position thereof andaunidirectional communication from said conduit to said casing when saidslide valve is movedrinrthe other direction from said neutral positionthereof, means operative by a pressure at'least substantiallyproportional to therpressure in said casing for urging said slide valvein said first men- 8 said compressor unit including two compressorelements, a compressor piston and a compressor cylinder, one movable-inthe other, each of said compressor elements being fixed with respecttoone of said motor elements, respectively, a casing fixed with respectto said motor cylinder for feeding compressed air thereto,saidcompressor elements forming between them an air compressionchamberycheck valve means for admitting air from the atmosphere intosaid air compression chamber on every intioned direction, means forminga space; means for feed- 7 ing said space with air under a pressurevariable in the same way as the mass of air insaid cushion chamber,

means operative by the pressure in said space for urging said slidevalve in said second mentioned direction, a cylinder fixed with respectto said casing, a piston fitting slidably in said last mentionedcylinder and dividing itinto two chambers, a first one ,and a secondone, conduit means for connecting said first chamber with said aircushion, conduit means for connecting said second chamber with saidspace, a rod slidable axially in said last mentioned cylinder, said rodbearing against said last men'- limiting'said second chamber, one end-ofsaid rod bearing against said piston, a spring interposed between saidend of said rodand said end wall of said last mentioned cylinder forurging said last mentioned piston in the same direction as the airpressure in said second chamber, a

crease ofyolume of said air compression chamber, check valve means fordelivering compressed airfrom said air compression chamber to saidcasing on every reduction of volume of said air compression chamber,said compressor elements forming between them an air cushion chamber thevolume of which is reduced on every increase of volume of said fuelcombustion chamber, whereby expansion of said air cushion produces everyreturn stroke 7 ofrsaid motor piston, a conduit having one end thereofin communication with said air cushion chamber, a stabiliser valvemounted to control the communication between the other end of saidconduit and said casing, said stabiliser valve including a cylindricalhousing, a hollow slide valve slidable in said casing and having aneutral position therein andcheck ,valve means carried by said slidevalve arranged to open a unidirectionalcommunication from said casing,to said conduit when said slide valve is moved in one direction fromsaid neutral position thereof and a unidirectional communication fromsaid conduit to said casing when said slide valve is moved inthe otherdirection from said neutral position thereof, means operative by a;pressure at least substantially proportional to the pressure in saidcasing for urging said slide valve in said first mentioned direction,means forming a variable volume space, conduit means between said spaceand said air cushion chamber including a throttled section, meansoperative by the pressure in said space for urging said slide valve insaid second mentioned direction, a cylinder fixed with respect to saidcasing, a piston fitting slidably in said last mentioned cylinder anddividing it into two chambers, a first one and a second one, conduitmeans for connecting said first chamber with said air cushion chamber,said last vmentioned conduit means including a throttled section,conduit means for connecting said second chamber with said space, a rodslidable axially in said last mentioned tioned piston, said rodextending slidably with a fiuidtightfit through the end wall of saidlast mentioned cylinder:

cylinder, said rod bearing against said last mentioned piston, said rodextending slidably witha fiuidtight fit through the end Wall of said'last mentioned cylinder limiting said second chamber, one end of saidrodbearing against said piston,a spring interposed between said end ofsaid rod and said end wall of said last mentioned cylinder for urgingsaid last mentioned piston in the same direction as the air pressure insaid second chamber, a sleeve slidably sleeve slidably fitting on saidmama rod being provided with a longitudinal conduit having at one endthereof an opening in said second chamber and at the other end thereofan opening adjacent'to said sleeve so as to be controlled by it, andmeans for operatively connecting said sleeve with said means forcontrolling said fuel feed means arranged to tend to reduce thefreecross section of said second mentioned opening when said means forcontrolling said fuel feed means is moved in the direction,

tending to reduce the feed of fuel and to tend to increase said freecross section when the feed of fuelfis caused to be'increased. i I

. 3. A free piston auto-generator which comprises, in combination, amotor unit and a compressor unit, said motor unit including two motorelements, a motor piston and a motorvcylinder, one movable in the otherto form between them a variable volume fuel combustion chamber, fuelfeed means opening into said fuel combustion chamber, means forcontrolling said fuel feed means,

fitting on said rod, said rod' being provided'witha longitudinal conduithaving at one end thereof an opening in said, second'chamber' and at theother end thereof an opening adjacent to 'said sleeve so as to becontrolled by it, and means for operatively connecting said sleeve withsaid .means for controliing'said fuel feed means arranged to tend toreduce the free cross section of said second mentioned opening when saidmeans for controlling said fuel feed means is moved in the directiontending to reduce the feed of fuel and to tend to increase "said freecross section when the feed of fuel is caused to be increased.

References Cited by the Examiner UNITED STATES PATENTS i 3,038,298 6/62Horgen 6()-13

1. A FREE PISTON AUTO-GENERATOR WHICH COMPRISES, IN COMBINATION, A MOTORUNIT AND A COMPRESSOR UNIT, SAID MOTOR UNIT INCLUDING TWO MOTORELEMENTS, A MOTOR PISTON AND A MOTOR CYLINDER, ONE MOVABLE IN THE OTHERTO FORM BETWEEN THEM A VARIABLE VOLUME FUEL COMBUSTION CHAMBER, FUELFEED MEANS OPENING INTO SAID FUEL COMBUSTION CHAMBER, MEANS FORCONTROLLING SAID FUEL FEED MEANS, SAID COMPRESSOR UNIT INCLUDING TWOCOMPRESSOR ELEMENTS, A COMPRESSOR PISTON AND A COMPRESSOR CYLINDER, ONEMOVABLE IN THE OTHER, EACH OF SAID COMPRESSOR ELEMENTS BEING FIXED WITHRESPECT TO ONE OF SAID MOTOR ELEMENTS, RESPECTIVELY, A CASING FIXED WITHRESPECT TO SAID MOTOR CYLINDER, FOR FEEDING COMPRESSED AIR THERETO, SAIDCOMPRESSOR ELEMENTS FORMING BETWEEN THEM AN AIR COMPRESSION CHAMBER,CHECK VALVE MEANS FOR ADMITTING AIR FROM THE ATMOSPHERE INTO SAID AIRCOMPRESSION CHAMBER ON EVERY INCREASE OF VOLUME OF SAID AIR COMPRESSIONCHAMBER, CHECK VALVE MEANS FOR DELIVERING COMPRESSED AIR FROM SAID AIRCOMPRESSION CHAMBER TO SAID CASING ON EVERY REDUCTION OF VOLUME OF SAIDAIR COMPRESSION CHAMBER, SAID COMPRESSOR ELEMENTS FORMING BETWEEN THEMAN AIR CUSHION CHAMBER THE VOLUME OF WHICH IS REDUCED ON EVERY INCREASEOF VOLUME OF SAID FUEL COMBUSTION CHAMBER, WHEREBY EXPANSION OF SAID AIRCUSHION PRODUCES EVERY RETURN STROKE OF SAID MOTOR PISTON, A CONDUITHAVING ONE END THEREOF IN COMMUNICATION WITH SAID AIR CUSHION CHAMBER, ASTABILISER VALVE MOUNTED TO CONTROL THE COMMUNICATION BETWEEN THE OTHEREND OF SAID CONDUIT AND SAID CASING, SAID STABILISER VALVE INCLUDING ACYLINDRICAL HOUSING, A HOLLOW SLIDE VALVE SLIDABLE IN SAID CASING ANDHAVING A NEUTRAL POSITION THEREIN AND CHECK VALVE MEANS CARRIED BY SAIDSLIDE VALVE ARRANGED TO OPEN A UNDIRECTIONAL COMMUNICATION FROM SAIDCASING TO SAID CONDUIT WHEN SAID SLIDE VALVE IS MOVED IN ONE DIRECTIONFROM SAID NEUTRAL POSITION THEREOF AND A UNDIRECTIONAL COMMUNICATIONFROM SAID CONDUIT TO SAID CASING WHEN SAID SLIDE VALVE IS MOVED IN THEOTHER DIRECTION FROM SAID NEUTRAL POSITION THEREOF, MEANS OPERATIVE BY APRESSURE AT LEAST SUBSTANTIALLY PROPORTIONAL TO THE PRESSURE IN SAIDCASING FOR URGING SAID SLIDE VALVE IN SAID FIRST MENTIONED DIRECTION,MEANS FORMING A SPACE CONTAINING AIR UNDER PRESSURE SUPPLIED FROM SAIDAIR CUSHION CHAMBER, MEANS OPERATIVE BY THE PRESSURE IN SAID SPACE FORURGING SAID SLIDE VALVE IN SAID SECOND MENTIONED DIRECTION, VARIABLE AIRLEAK MEANS IN COMMUNICATION WITH SAID SPACE AND MEANS FOR CONTROLLINGSAID AIR LEAK MEANS OPERATIVE BY SAID MEANS FOR CONTROLLING SAID FUELFEED MEANS, SAID MEANS FOR CONTROLLING SAID AIR LEAK MEANS BEINGARRANGED TO TEND TO INCREASE THE FREE CROSS SECTION OF SAID AIR LEAKMEANS WHEN SAID MEANS FOR CONTROLLING SAID FUEL MEANS IS CAUSED TOINCREASE THE FEED OF FUEL AND TO TEND TO REDUCE SAID FREE CROSS SECTIONWHEN THE FEED OF FUEL IS DECREASED.